Process of treating lubricating oil stock with a phosphorus sulfide and a base and the resulting products



United States Patent f PROCESS OF TREATING LUBRICA-TING STOCK WITH A PHOSPHORUS SULFIDE AND A BASE AND THE RESULTING PROD- UCTS Harvey E. Alford, Amherst, and John D. Bartleson, Beachwood Village, Ohio, assignors to The Standard Oil Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application August 20, 1952',- Serial No. 305,513

8 Claims. (Cl. 252-323) This invention relates to a process of treating hydrocarbon base lubricating oil stocks and, more particularly, to a process of treating such stocks with a small amount of a phosphorus sulfide and a base to form lubricants having improved properties and to the resulting improved lubricants.

Hydrocarbon base stocks are generally employed in the preparation of commercially used lubricants. The stocks may be synthetically prepared or may be derived from natural sources, such as petroleum. In order to produce a lubricant having desirable characteristics; particularly dctergency, lubricating oil additives must be ineluded with the hydrocarbon base stocks. Solvent-extracted oils, for example, are notably corrosive, and if this is to' be corrected and detergen'cy imparted" one' or more additives or a multifunctional additive may be necessary. The employment of such additives is associated with an increase in cost of the finished lubricant, which is regarded as a necessary expense, but desirably to be avoided. It would be preferable to prepare a finished lubricant directly from the hydrocarbon base stock by chemically finishing or refining the stock to provide the desired properties at a commercially interesting cost.

In U. S. Patent No. 2,560,546, dated July 17, 1951, to John D. Bartleson, a process of treating solvent-re= fined hydrocarbon base lubricating oil stocks has been described which overcomes the corrosion characteristics thereof and imparts detergency thereto, thus avoiding the need for incorporating additives in such stocks. Ac' cording to the process outlined in that patent, the hydrocarbon lubricating oil stock is reacted with a small amount of phosphorus sulfide and then with a base to produce a stock having good antioxidant and corrosion inhibition properties and, in addition, a high detergency. Such lubricants are suitable for use under various conditions, including high temperatures or high pressures or both, as for instance, in an internal combustion engine operating at high temperatures and in which the lubricantis in close contact with metallic surfaces, metal compounds and high temperature gases. They also are suitable for use in extreme pressure lubricants, e. g., in oilsand greases containing the same. The resulting reaction products thus can be characterized as chemically finished' or refined improved lubricants, relative to the untreated solvent-refined hydrocarbon base lubricating oil stock.

In the preparation of additives according'to the process may form which outlined in the Bartleson patent, sludge is tacky and resinous in nature, having a tendency to adhere to the Walls of the reaction vessel and to clog the filter when the reaction mixture is filteredto separate sludge and unreacted materials. The sludge may occlude 2 oil, and reduce the yield. This problem makes the proc ess less attractive from the commercial standpoint.

In accordance wtihthe instant invention, the reaction between the hydrocarbon base lubricating oil stock and the phosphorus sulfide is carriedo'ut while blowing an inert gas through the reaction mixture during' the reaction. Under these conditions sludge which forms in the course of the reaction with phosphorus sulfide is hard and nontacky in nature, easily removed by filtratior'1', and' dis playing little or no tendency to adhere to the Walls of the reaction vessel. In this way the sludge problemis satisfactorily resolved. At the same time, other desirable characteristics of the reaction product, such as sulfur content, may be improved.

The product thus obtained is a very useful lubricant. As set forth in the B artlesonPatent No. 2,560,546, it can be treated with a base to form a metal derivative of desirable properties. In accordance with the instant invention, a further process improvement is made in this treatment by reacting the phosphorus sulfide-lubricating o'il reaction product with a base while blowing an inert gas therethrough and also in the presence of water. This step is optional, but is preferred since the alkaline number, sulfur content and ash content of the resulting product thereby may be increased, suggesting'improved dete'rgency and' anti-acid wear characteristics in se'rvice. The reaction product obtained after neutralization with a base also" has a high stability against hydrogen sulfide formation, even in the presence of water, at temperatures as high as 150 F. p 4

The reaction of the hydrocarbon base stock with the phosphorus sulfide can be carried: out as set forth in the aforesaid U. 8'. Patent No. 2,560,546 to John D. Bartleso'n'. Thus, the reaction can he conducted with direct admixture of the stock with the phosphorus sulfide or, if desired, by their admixture in the presence of a diluent which may be subsequently removed. Generally, a dil uent is not necessary. The reaction usually is complete in about ten hours" or less, generally from one to two hours. The reaction time is a" function of the temperatu're, the amount of sulfide that is to react, the degree of subdivision of the reactants, the efficiency of mixing and the concentration of the reactants in the diluent, it one is present. 7

The invention is applicable particularly to solve'nt-refined hydrocarbon base lubricating oil stocks, i. e., stocks treated in accordance with conventional modern methods of solvent refining lubricating oils. The oil may' be a fluid hydrocarbon lubricating oil: base stock having a viscosity at F. of 10 to 500 centistokes, such as is matic; unsaturated and low viscosity index materials, and

these are se aratea out. A clay treatment may or may not follow, and is desirable but not essential. Where necessary, a separate propane or the like deasphalting treatment may be used" in connection with the solventrefihin'g Tlieifive'rition anonapplicahle toother refined lubrl cant stocks, such as acid-treated stocks.

polymerization, dehydrogenation and The solvent refining process is well The hydrocarbon lubricating stock is reacted with the phosphorus sulfide in a ratio within the range from about 0.1 to about 0.75% by weight, based on the weight of the stock, desirably about 0.25 to about 0.6% and preferably about 0.3 to about 0.5%. Higher amounts of the sulfide give products which may be inferior to the hydrocarbon as to viscosity increase. Generally at least 0.1% should be used to achieve the desired result, although smaller amounts show some improvement.

Any phosphorus sulfide reactive with hydrocarbon base lubricating oil stocks can be used. Phosphorus pentasulfide is most readily available and least expensive and therefore would most ordinarily be employed and is used in the illustrative examples which follow. However, other phosphorus sulfides can be used with good results, such as phosphorus sesquisulfide, P483, phosphorus trisulfide, P283, phosphorus heptasulfide, P487, and phosphorus disulfide, P386. The reaction temperature varies with the hydrocarbon stock. Generally the treatment should be at least at 275 F. A temperature in the range of about 300 to about 450 F. is preferred in many cases. The maximum temperature is that at which the reaction product or the reactants would be decomposed.

During the reaction in accordance with the invention an inert gas is blown through the reaction mixture. The rate at which the gas is blown through depends upon the volume of the reaction mixture and the reaction temperature. Since the gas is nonreactive, the amount used is not critical in any way, but usually a volume of 0.05 to 0.5 volume per volume of reaction mixture per minute would be used. The maximum blowing rate would be dictated by the size of the equipment and the extent of disturbance of the reaction mixture by the gas. A sufficient amount should be blown through to remove HzS gas as it is formed. Since the rates of reaction and of H28 formation increase with the reaction temperature, more gas is required at the higher reaction temperatures.

A distinction is to be made between effecting the reaction under a blanket of inert gas and blowing inert gas through the reaction mixture. An inert gas blanket will not permit the obtention of the desirable results secured by blowing the gas through the mixture and, in fact, the final product may contain a larger amount of sludge of the tacky, resinous character previously noted as objectionable than would be obtained in its absence. The physical properties and engine performance characteristics of the products prepared under an inert gas blanket and by blowing an inert gas through the mixture are equivalent, showing that the blowing step does no harm, while improving the sludge characteristics.

Any inert gas nonreactive with the reaction products or reactants can be used, for example, nitrogen, argon, helium, and refinery gases chiefly composed of lower saturated paraflinic hydrocarbons. Refinery gases and nitrogen usually would be used because of their low cost and their existence in plentiful supply.

The reason for the efiectiveness of the inert gas is not as yet fully understood. Since it appears that the gas removes hydrogen sulfide as it forms, it would be expected thereby to shift the reaction equilibrium in the direction towards completion of the reaction to form the desired phosphorus sulfide lubricant stock reaction product. This may minimize side reactions of H28, which may be responsible for the formation of the sticky, resinous sludge previously noted as objectionable. This theory has been confirmed in part by experiments involving the blowing of hydrogen sulfide gas through the reaction mixture. When this is done, practically no reaction occurs between the phosphorus sulfide and the lubricating stock, as demonstrated by low sulfur content, ash content and alkaline numb er.

Upon completion of the reaction, the mixture preferably is centrifuged or filtered to remove by-products, sludge or other material. Due to the blowing of inert gas through the reaction mixture, a sludge having a hard, nontacky character is formed, easily separated from the reaction mixture by filtration. A volatile diluent, if present, can be removed by evaporation or distillation.

The phosphorus sulfide-refined stock can be used as such, and has very desirable lubricant properties. If a detergent oil is required, the product can be neutralized by treatment with a base to form the corresponding metal derivative. The procedure set forth in U. S. Patent No. 2,560,546 can be followed to prepare the metal derivatives.

The metal derivatives may be prepared from one or more metal compounds, such as sulfides, oxides, hydroxides, carbides and cyanarnides. The preferred compounds are of metals selected from groups I, II and III of the periodic table, such as potassium, sodium, zinc, calcium, barium and aluminum. The alkali and alkaline earth metals are preferred. For some purposes the derivatives of the heavier metals below zinc in the electromotive series, such as chromium, cadmium, tin, lead, antimony, bismuth, arsenic and the like, can be prepared from the corresponding metal compounds.

In the treatment with the metal compound to form the metal derivative, the reaction may be conducted at temperatures in the range from about to about 400 F., a temperature in the range of about 180 to 350 F. being preferred. If the sulfide-refined stock has been subjected to a temperature of at least 300 F., alternatively the metal derivative may be prepared at or subjected to this temperature.

The reaction can be carried out in the presence of an inert gas, desirably by blowing it through the reaction mixture, as in the reaction of phosphorus sulfide with the oil. This assists in the dissipation of water liberated in the neutralization. Here also, blowing an inert gas may result in improving the characteristics of any sludge which forms, yielding a hard, nontacky, easily filtered sludge. Ash and alkaline number may also be higher.

At least about 0.25 equivalent of metal compound is used per mole of the sulfide used in the sulfide-refined stock, preferably about 1.0 to about 8.0 equivalents. There is no critical upper limit to the amount of base that can be used, except that more than can react with the solvent-refined stock would not be used. In many cases more than eight equivalents, up to 10.5 or 12 equivalents, would be used to achieve a higher alkaline number, ash and sulfur content. If the antioxidant and corrosion inhibition properties of the metal derivative are wanting, any antioxidant can be added to the oil. I Expressed on a weight basis, the amount of base used should be at least about one part to each part of sulfide used in the solvent-refined stock, preferably two to three parts of base to each part of sulfide.

The reaction between the base and the sulfide-treated stock is preferably, but not necessarily, carried out in the presence of water, because of the additional improvement in properties thereby obtained, especially in H25 storage stability and in color (0. D.). An amount of water in excess of 1% is desirable to obtain an observable improvement. When the neutralization is effected in the presence of about 3 to 5% water, the product may be superior in ash and alkaline number to that obtained without water. The high ash content indicates an improved detergency, which is essential for clean engine operation, and the high alkaline number indicates an improved ability to combat acid action, thus reducing engine wear. The upper limit of water which would be employed is not critical, but would be established by the foaming problem experienced in heating large batches of materials in the presence of large quantities of water. Usually from 3 to 5% water would be employed to achieve an improvement in detergency and anti-acid characteristics while minimizing foaming difiiculties.

In order to illustrate some of the advantages of the invention, but in no sense as a limitation thereof, the following specific embodiments are included.

EXAMPLES 1 TO 4 In these examples the hydrocarbon stock is a conventional solvent-extracted lubricating oil base stock pregests that a somewhat more complete reaction is obtained in accordance with the method of the invention, particularly during the neutralization step.

Each of the above lubricants was subjected to the pared by blending 88.5 parts of No. 300 neutral oil (300 5 Polyveriform test (Anal. Chem. 21, 737 (1949)), a U at 100 and 5 parts each of 7 7 SSU laboratory test Whose results are closely correlated with at 2100 R) and 250 (250 SSU at 0 R) bright the L-4 Chevrolet engine test. The data obtained are reproduced in Table III. stocks. This is a good grade of solvent-refined oil, SAE Table "I No. 20, available on the market, and is typical of such 10 a product Example No Blank 1 2 3 4 The phosphorus pentasulfide is mixed with the lubricat- N N and M 3 Z 1 mg 011 in amounts 1nd1cated in Table I and reacted for N1 bubbled line gas bubbled p blanket during bubbled during the time indicated at the temperature indicated and at reaction during reaction atmospheric pressure. The gas indicated was bubbled reactlon through the reaction mixture at a rate of 0.1 volume per 8 cmmsgofl 73 Z 4 mg 8.2 is. no.,100 1 .0 1.0 51.1 6.7 volume of mixture per nnnut; ghroughout thereactjlon. g t l gf 392 084 L67 1 89 L29 e ta S11] r x1 e co talmn a out en inso OS The has used was p0 S m y o n 20 mgIHSJlO gms. 011.... 57.7 9 4.5 3.2 2.6 12% water and therefore 88% active KOH. How- Lacquer A A A A ever, all weight percents in the table are the amount of Sludge A A A A A solid potassium hydroxide, which contains water, used. is A E.NO 20 motor on Table l Ex- Per- Per- Gas Blown Reaction Reaction ample cent cent Through Time, Tern- Remarks No. P285 KOH Reaction Hours perature,

Mixture F.

0.4 Nitrngen 1 300 Some sludge formed. Filter aid (2%) required for filter- 0.8 2 250 2% filter aid added: prodnot filtered. 0.4 Nitrogen. l 300 Very little sludge formed. Filtered easily without 2 filter aid.

0.8 2 250 Filteration rapid without ter aid. 0.4 Nitrogen l 300 Very little sludge formed. Filtered easily without 3 filter aid.

0. 8 Line gas 2 250 Filteration very rapid without filter aid. 0.4 Air 1 300 A considerable amount of sludge formed which adhered to the sides or the 4 flask. The material would not filter without filter aid. 0.8 Air 2 250 Would not filter without filter aid.

1 Under a nitrogen blanket. Gas not blown through mixture.

The KOH neutralization was carried out without addition of water.

The products obtained analyzed as follows:

Table 11 Example No 1 2 3 4 N2 N and Air Na bubbled line gas bubbled blanket during bubbled during reaction during reaction reaction Percent S 1 0. 29 0. 325 0. 33 0. 34 Percent It..- 0.107 0.105 Percent Ash 0. 43 0. 563 v 0. 49 0. 385 "r- 97.1 75.1 90.6 -69.-5 pH 10.1 12.2 11.15 7.0 Alkaline No 1.02 1.85 1.70 0.59

l ilfhese analyses include 0.21% sulfur which is present in the base stock itse Example 1, prepared under a nitrogen blanket, and Example 4, in which air, which is not an inert gas, was bubbled through the reaction mixture, each contained greater amounts of sludge and would not filter without filter aid. Examples 2 and 3, which follow the method of the invention, gave excellent yields and very small quantities of sludge of a hard, nontacky character, and were rapidly filtered without the use of filter aid.

Table 11 gives the analyses of the reaction products. The ash, the alkaline number and pH are higher 'for Examples 2 and 3 than for Examples 1 and 4, while sulfur and optical density compare favorably. This sug- The treated oils of Examples 2 and 3 have a much better performance than the blank, and are approximately as good as that of Example 1.

The odor stability also is satisfactory, as the following In obtaining the data of Table IV, the lubricant was stored at room temperature for the time indicated, in the one case in the absence of water and in the other in the presence of 1% water.

EXAMPLE 5 8850 g. of 300 solvent-extracted neutral oil (300 SSU at F.), 500 g. of 78 bright stock (78 SSU at 210 F.), 500 g. of 250 bright stock (250 SSU at 210 F.) and 39.4 g. (0.4%) of P285 were reacted for one hour at 300 F. Nitrogen was bubbled through the mixture during the reaction. The mixture was then filtered, fildifficulty was encountered with foaming.

mixture was heated slowly to 250 F. Nitrogen was No After two hours at 250 F., 2% filter aid was added and the product filtered rapidly. Percent yield=99.3.

EXAMPLE 6 To 600 g. of the PzSs-treated oil described in Example were added 18 g. of water (3%) and 4.8 g. flake KOH. The mixture was heated slowly to 250 F. No dilficulty was experienced with foaming. Nitrogen was passed through the mixture during the reaction. After bubbled through the mixture during the reaction.

two hours at 250 F., 2% filter aid was added and the product filtered rapidly. Percent yield=99.3.

EXAMPLE 7 EXAMPLE 8 3.3 g. of P285 and 829 g. of S. A. E. No. 20 motor oil (88.5 parts No. 300 solvent-extracted neutral oil (300 SSU at 100 F.), 5 parts of 78 (78 SSU at 210 F.) bright stock and 5 parts of 250 bright stock (250 SSU at 210 F.)) were heated for one hour at 300 F. while bubbling nitrogen through the mixture. The sludge was.

hard and nontacky, and the product filtered easily. Per cent yield=99.0.

To 600 g. of the above was added 4.8 g. of flake KOH. The mixture was heated for two hours at 250 F. while bubbling N2. The product was filtered. Percent yield: 98.8.

EXAMPLE 9 To 600 g. of the PzSs-treated oil described in Example 5 was added 6 g. (1%) of water. The mixture was heated slowly to 180 F., and then nitrogen was passed through for one hour at 180 F. The mixture was then heated slowly to 250 F. where it was held for one hour, still with N2 bubbling through. There was no difiiculty with foaming. The product Was filtered. Percent yield: 99.2.

To 300 g. of the above product was added 2.4 g. of flake KOH, and the reactants heated at 250 F. for two hours. Nitrogen wa bubbled through during the reaction. Percent yield=99.3.

EXAMPLE To 600 g. of the PzSs-treated oil described in Example 5 was added 18 g. (3%) water. The mixture was heated slowly with stirring to 180 F. Nitrogen was bubbled into the mixture during the reaction. After one hour at 180 F. the mixture was heated slowly to 250 P. where it was held for one hour, still with N2 passing through. The product was filtered. Percent yield==99.2. To 300 g. of the above was added 2.4 g. of flake KOH. The mixture was reacted at 250 F. for two hours while bubbling N2 through. Filtration was rapid without the use of filter aid. Percent yield=99.6.

EXAMPLE 11 30 g. (5%) of water was reacted with 600 g. of PzSstreated oil in the manner described for Example 10. Percent yield=99.3.

300 g. of this product and 2.4 g. of flake KOH were The material filtered rapidly without filter aid.

heated for two hours with stirring at 250 F. Nitrogen was passed into the mixture during the reaction. Filtration was very rapid without the use of filter aid. Percent yield=99.3.

V EXAMPLE 12 3634 g. of S. A. E. No. motor oil (88.5 parts 300 solvent-extracted neutral oil (300 SSU at 100 F.), 5 parts 78 bright stock (78 SSU at 210 F.) and 5 parts 250 solvent-extracted bright stock (250 SSU at 210 F were reacted with 14.5 g. (0.4%) of Pass for one hour at 300 F. Nitrogen was bubbled into the mixture during the reaction. The sludge was hard and nontacky, and the product was filtered readily. Percent yield=99.7.

600 g. of the above product and 4.8 g. (0.8%) of flake KOH were reacted for four hours at 250 F. Nitrogen was bubbled into the mixture during the reaction.

The reaction products of Examples 5 to 12 were analyzed with the following results:

Table V Water Added Water Roasted Before During Neutral- Neutralization izatlon Stop Example No 5 6 7 8 9 10 11 12 Percent water added 1 3 5 0 1 3 5 0 Percent S 0. 28 0.35 0. 33 0.33 0. 33 0. 0.20 0. 35 Percent P 0.10 0. l0 0. 09 0. 10 0. 10 0. 10 0. 94 0. 07 Percent ash (S0 0. 47 0. 60 0. 70 0. 56 0. 0. 13 0. 43 0. (i0 O.D 63.7 78.1 73.1 75.1 81.S113.4112.7 84.2 pH 10. 72 11. 11.9 12. 2 9. 10. 50 10. 0210. Alkaline No 1. 26 1. 65 2.13 1.85 1. 20 1. 27 1. 30 1.78

The presence of water primarily attects ash content and alkaline number. With 1% water, both ash and alkaline number are considerably lower than in the case of preparations made with larger amounts of water. At 3% water the product is superior in ash and alkaline number to that obtained at 1% water, while with 5% water the product is even better. Thus amounts of water in excess of 3% are indicated, with 5% being the optimum. The high ash and alkaline number of the 5% product indicates improved detergency essential for a clean engine operation and efiectiveness in combating acid acition, thus reducing engine wear.

Oils treated with water after the phosphorous sulfide reaction but before the neutralization do not possess the improved characteristics of the oils of the invention. Ash, pH and alkaline number are all lower, while the color is considerably darker. It is thus evident that the presence of water during neutralization is required to improve the product, and that water added before neutralization is inefiective.

A comparison of Tables 11 and V shows the benefits obtained by preparing the metal derivative in the presence of water.

Table VI gives the results of hydrogen sulfide stability in which the oil was stored at F. for the time indicated in the table. It is evident from this data that Examples 6 and 7 are far superior to any of the other oils tested, showing the improvement obtainable by carrying out the neutralization in the presence of 3 and 5% water, respectively. Oils in which the water is reacted separately prior to neutralization are very poor in storage stability.

Table VI Example N0. Percent Water Added Time belore positive 11 8 1% during neut 64 hrs.

D during nent 636 hrs.

7 during neut.

OUIM

seq

' 7 before neut. 9 before neut. 9 before neut.

The S in HzS is thought to be derived from the P-SP bonds. It is believed that the two PSP bonds are not of equal bond strength. One is easily broken, requiring only a small amount of energy, and this accounts for the acid number of the compound. Assuming that one or both of these bonds are broken in the course of neutralization, the following mixture of two compounds can be postulated for the neutralized material: (1) s s R-l S-1 R R-i K The second of these could not form hydrogen sulfide since there is no P-S-P bond, but the first of the two could.

Storage at room temperature, even in the presence of water, does not supply the energy required to break the remaining PAS-P bond to form HzS, but when the oil is stored at 150 F., the extra energy is more readily available and hydrolysis occurs. It is thought that in the presence of water in the neutralization reaction both PqSP bonds are broken and the neutralized oil would not then be a mixture of the two components suggested above, but a substantially pure composition of the second, which cannot form H28.

If desired, the improved lubricants of the invention can be used in blends together with other lubricants or other lubricant agents, such as soap and the like in a grease.

An agent for improving the clarity of the oil may be included, e. g., lauryl alcohol and the like. Agents for preventing foaming may also be present, e. g., tetraamyl silicate, an alkyl orthocarbonate, orthoformate or orthoacetate or a polyakyl silicone oil.

All parts and percentages in the specification and claims are by weight.

We claim:

1. A method of processing lubricating oil which comprises treating said stock with an amount of phosphorus sulfide within the range from about 0.1 to about 0.75% while blowing an inert gas through the reaction mixture at a temperature within the range of at least 275 F. to about 450 F. at which the lubricating oil stock and the phosphorus sulfide react.

2. A process in accordance with claim 1 which includes further treating the reaction product with a base in an amount Within the range of at least about 0.25 to about 12 equivalents per mole of the phosphorus sulfide at a temperature in the range from about to about 400 F.

3. A process in accordance with claim 2 which includes treating with a base in the presence of water.

4. The method of claim 3 wherein from 1 to 5% water is present during the neutralization reaction.

5. A process in accordance with claim 2 which includes blowing an inert gas through the reaction mixture while treating the reaction product with a base.

6. The method of claim 1 wherein the stock is treated at a temperature in the range of about 275 to 350 F.

7. The method of claim 1 wherein the stock is treated with an amount of phosphorus pentasulfide in the range of about 0.4 to about 0.6% and then with an amount of potassium hydroxide in the range of about 0.25 to about 12 equivalents per mole of the phosphorus pentasulfide.

8. The method of claim 1 wherein the inert gas is nitrogen.

References Cited in the file of this patent UNITED STATES PATENTS 2,316,091 White Apr. 6, 1943 2,466,408 Funk Apr. 5, 1949 2,476,813 Buckmann July 19, 1949 2,560,546 Bartleson July 17, 1951 2,636,858 Jones Apr. 28, 1953 

1. A METHOD OF PROCESSING LUBRICATING OIL WHICH COMPRISES TREATING SAID STOCK WITH AN AMOUNT OF PHOSPHORUS SULFIDE WITHIN THE RANGE FROM ABOUT 0.1 TO ABOUT 0.75% WHILE BLOWING AN INERT GAS THROUGH THE REACTION MIXTURE AT A TEMPERATURE WITHIN THE RANGE OF AT LEAST 275* F. TO ABOUT 450* F. AT WHICH THE LUBRICATING OIL STOCK AND THE PHOSPHORUS SULFIDE REACT. 